Anthony Olivieri

Thin Au surface plasmon waveguide Schottky detectors on p-Si.

Surface plasmon sub-bandgap Schottky detectors based on an asymmetric Au stripe waveguide on p-Si are investigated theoretically and experimentally at free-space wavelengths of λ(0) = 1310 and 1550 nm. Au on p-Si produces a low Schottky barrier (0.33 eV), which improves the internal quantum efficiency. Thick and thin Au stripes are compared, with the latter increasing the hot hole emission probability relative to the former, and thus also improving the internal quantum efficiency. Two excitation schemes are considered: end facet illumination which launches surface plasmons on the detector, and top illumination which does not. Both schemes are implemented using a piezoelectric positioner that is programmed to scan the detection area in steps of 100-200 nm, thus enabling the acquisition of high-resolution photocurrent maps. The surface plasmon detectors yield a responsivity of ~1 mA W(-1), ~2× larger than the same detectors under top illumination, due to the absorption of surface plasmons. We compare the measurements with theoretical results for both excitation schemes and estimate the hot hole attenuation length in our Au stripes to be ~23 nm.

Plasmonic Nanostructured Metal–Oxide–Semiconductor Reflection Modulators

We propose a plasmonic surface that produces an electrically controlled reflectance as a high-speed intensity modulator. The device is conceived as a metal-oxide-semiconductor capacitor on silicon with its metal structured as a thin patch bearing a contiguous nanoscale grating. The metal structure serves multiple functions as a driving electrode and as a grating coupler for perpendicularly incident p-polarized light to surface plasmons supported by the patch. Modulation is produced by charging and discharging the capacitor and exploiting the carrier refraction effect in silicon along with the high sensitivity of strongly confined surface plasmons to index perturbations. The area of the modulator is set by the area of the incident beam, leading to a very compact device for a strongly focused beam (∼2.5 μm in diameter). Theoretically, the modulator can operate over a broad electrical bandwidth (tens of gigahertz) with a modulation depth of 3 to 6%, a loss of 3 to 4 dB, and an optical bandwidth of about 50 nm. About 1000 modulators can be integrated over a 50 mm(2) area producing an aggregate electro-optic modulation rate in excess of 1 Tb/s. We demonstrate experimentally modulators operating at telecommunications wavelengths, fabricated as nanostructured Au/HfO2/p-Si capacitors. The modulators break conceptually from waveguide-based devices and belong to the same class of devices as surface photodetectors and vertical cavity surface-emitting lasers.

Subbandgap Asymmetric Surface Plasmon Waveguide Schottky Detectors on Silicon

Silicon-based surface-plasmon subbandgap detectors integrated with an asymmetric metal stripe are investigated for different metals, modes, and wavelengths of operation. Low-order bound modes supported by Al and Au stripes cladded below by silicon and covered by air are studied at the infrared wavelengths of 1310 and 1550 nm. Input optical power is end-fire coupled into the modes supported by the stripe, resulting in the total absorption of coupled power over a short length. The absorbed power creates excited carriers in the metal throughout the modal absorption volume, which can cross the Schottky barrier and become collected as photocurrent (internal photoemission). Measurements obtained for Au on n-type Si support predicted trends. The device has promise for applications in short-reach high-speed optical interconnects and silicon-based nanophotonics.

Enhanced Raman scattering in graphene by plasmonic resonant Stokes emission

Abstract Exploiting surface plasmon polaritons to enhance interactions between graphene and light has recently attracted much interest. In particular, nonlinear optical processes in graphene can be dramatically enhanced and controlled by plasmonic nanostructures. This work demonstrates Raman scattering enhancement in graphene based on plasmonic resonant enhancement of the Stokes emission, and compares this mechanism with the conventional Raman enhancement by resonant pump absorption. Arrays of optical nanoantennas with different resonant frequency are utilized to independently identify the effects of each mechanism on Raman scattering in graphene via the measured enhancement factor and its spectral linewidth. We demonstrate that, while both mechanisms offer large enhancement factors (scattering cross-section gains of 160 and 20 for individual nanoantennas, respectively), they affect the graphene Raman spectrum quite differently. Our results provide a benchmark to assess and quantify the role and merit of each mechanism in surface-plasmon-mediated Raman scattering in graphene, and may be employed for design and realization of a variety of graphene optoelectronic devices involving nonlinear optical processes.

High-responsivity sub-bandgap hot-hole plasmonic Schottky detectors

In this paper we present a sub-bandgap photodetector consisting of a metal grating on a thin metal patch on silicon, which makes use of the enhancement produced by the excitation of surface plasmon polaritons at the metal-silicon interface. The grating is defined via e-beam lithography and Au lift-off on a Au patch defined beforehand by optical lithography on doped p-type silicon. The surface plasmon polaritons are absorbed by the metal, leading to the creation of hot holes that can cross into the silicon where they are collected as the photocurrent. Physical characterization of intermediate structure is provided along with responsivity measurements at telecom wavelengths. Results are promising in terms of responsivity, with a value of 13 mA/W measured at 1550 nm - this is among the highest values reported to date for sub-bandgap detectors based on internal photoemission. The Schottky photodetector can be used in, e.g., non-contact wafer probing or in short-reach optical communications applications.

Fabrication of a plasmonic modulator incorporating an overlaid grating coupler

The fabrication of a novel plasmonic reflection modulator is presented and described. The modulator includes plasmon excitation using a diffraction grating coupler and is based on a metal-insulator-semiconductor structure on silicon. Fabrication includes a thin thermal oxide, a plasmonic metal surface defined by optical lithography, a metal grating coupler defined by overlaid e-beam lithography, a passivation layer with metalized vias, and electrical contacts. Physical characterization of intermediate structures is provided along with modulation measurements at λ0 ∼ 1550 nm which verify the concept.

Guided bloch long-range surface plasmon polaritons

A few years ago, Konopsky showed that a one dimensional photonic crystal structure can be used on one side of a thin metal layer to mimic the optical properties of the material on the other side. Inspired by this approach and motivated by using LRSPP waveguides for biosensing, we propose and realized a thin metal stripe on a truncated SiO2/Ta2O5 multilayer stack to support a fully guided LRSPPs. These results further the attraction of metal stripe waveguides and LRSPPs for biosensing applications and more in general for LRSPP integrated optics.

On-chip nonlinear plasmonics with graphene-metal nanostructures

This work demonstrates coherent nonlinear interaction between surface plasmon polaritons (SPPs), supported by gold nanoresonators, and monolayer graphene. It is shown that the coupling to SPPs not only enhances the amplitude of the Raman scattering in graphene, but also affects the spectral characteristics of the Stokes emission by broadening and blue shifting the emission lineshape.

Plasmonic optoelectronics on silicon

Metallic nanostructures such as gratings or antennas operate as a coupling structure that couples incident light to surface plasmon polaritons (SPPs) propagating thereon or on an underlying thin metal film. When deposited on a semiconductor such as a Si substrate the nanostructures become useful as infrared intensity modulators or photodetectors, exploiting SPP-enhanced carrier refraction in Si, or SPP-enhanced internal photoemission, respectively. Various materials are considered, including materials that are standard for electronics.

Surface plasmon detectors on silicon

This paper outlines the experimental methods and results obtained from the testing of asymmetric gold surface plasmon waveguide detectors on an epitaxial silicon structure at optical wavelengths of 1550 nm and 1310 nm. Using end-fire coupling, responsivities of up to 0.88 mA/W at a 100 mV reverse bias were measured. The photo-detection mechanism is based on the internal photoelectric effect. The simple and compact design allow for these devices to be integrated and densely populated with Si-based optoelectronics. The ability to detect wavelengths below the bandgap of Si is also appealing. 2D responsivity maps are generated using piezoelectric positioners controlled using Labview.